What Is Contrast Therapy? The Science Behind the Practice
Dr. Susanna Søberg, PhD · soeberginstitute.com
Contrast therapy has become one of the most discussed practices in the global wellness space. Cold plunges, saunas, ice baths, steam rooms — the terminology can be confusing and the claims even more so.
I want to cut through the noise and give you the clear, honest scientific picture — because contrast therapy, when you understand what it actually is and how it actually works, is one of the most powerful physiological tools available to us.
And I say that not as someone who discovered it on social media. I say it as a scientist who has spent over 15 years studying exactly what it does to the human body.
The simple definition
Contrast therapy is the deliberate, structured alternation between cold exposure and heat exposure — for specific physiological effect.
The word structured is the key one. Contrast therapy is not simply getting cold and then warm. It is the application of thermal stress in a specific sequence, at specific intensities — with the structure of that sequence directly influencing the physiological outcome.
This is the central insight of the Søberg Principle — my peer-reviewed research published in Cell Reports Medicine in 2021. How you structure a contrast therapy session determines what your body does in response to it.
What the science actually shows
Cold exposure triggers brown fat activation, a significant norepinephrine surge, cardiovascular training, and immune system activation. Heat exposure activates heat shock proteins for cellular repair, produces cardiovascular conditioning, and supports nervous system recovery.
The deliberate alternation of these two states — done in a structured sequence — creates a combined effect greater than either cold or heat alone. It is a comprehensive training stimulus for the body’s regulatory systems simultaneously.
This is why I built the Thermalist® Method as a system — not as a single tip or a single protocol. The science of contrast therapy is too specific, too nuanced, and too individual to be reduced to a social media post.
The ancient practice validated by modern science
It is worth noting that contrast therapy is not new. Roman bathhouses alternated between hot and cold pools. Scandinavian sauna culture has included cold lake plunging for centuries. The traditional Finnish sauna practice almost always concludes with cold exposure.
What is new is the precision. We can now measure exactly what happens in the body during and after structured contrast therapy — and that precision is what makes it possible to practice it intelligently rather than simply enthusiastically.
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I cover the complete science of contrast therapy — including the Søberg Principle, brown fat activation, the nervous system effects, safety guidance, and how to build an effective practice — in the Thermalist® Method at Home course and the Cold Water Immersion Course at soeberginstitute.com.
→ Thermalist® Method at Home — soeberginstitute.com
→ Cold Water Immersion Course — soeberginstitute.com
The full science journal article on contrast therapy is also available on the Søberg Institute website for those who want the deeper read.
— Dr. Susanna Søberg
